Videocrypt
An Overview
Researched and written by Darren Ingram, author of Satnews
- Satnews.. the latest and non-Commercial satellite news -
Version 1.34 - 14.05.91
Note: This file acknowledges all trademarks and their respective
owners where mentioned in the text. All rights reserved (C) 1991.
--
Index:
Introduction
Requirements
Features and applications
Scrambling
Customers
Appendices
INTRODUCTION
Videocrypt is a pay-tv scrambling system jointly developed by Thom-
son Consumer Electronics and News Datacom. Over one million users
receive Videocrypt encrypted signals and this system, has to date,
remained secure from illicit decoder manufacturers, protecting the
revenue of Videocrypted television channels.
REQUIREMENTS
Videocrypt is a multi-standard encryption system which is suitable
for PAL, NTSC and SECAM transmissions. Language is no barrier for
Videocrypt with its capacity for multi-lingual transmissions and
broadcasts utilising a comprehensive on-screen instruction menu.
Features and applications
A smart card is the central key to the Videocrypt system, and the
card can be used for a variety of diverse applications. The card
is pre-coded to determine a users requirements and it can subse-
quently be addressed utilising the decoders logic to amend the users
services at the broadcasters will.
There are a number of broadcasting modes which the smart card can be
used within including:
Clear Mode
Signals sent in the clear are recognised by the decoder and
passed to the display without further processing.
Free Access
Pictures transmitted with an encryption key are delivered
directly to the display through the decoder.
Controlled Access
Access to encrypted pictures is determined by the level
of access authorised to the users smart card. No signals
will be transmitted in an unencrypted state without prior
authorisation.
Programmes can be tailored to usage with the Videocrypt system and
the system offers a flexible way for pay-tv operators. There are a
number of operations mode offered as standard including:
* Single or multiple subscriptions with many tier levels in one
channel
* Pay Per View (PPV) and impulse purchasing
* Thematic selection (enable all arts programming)
* Geographic limitation (restrict to a country/area)
* Single-event (throwaway cards)
* Parental Control (reception with card only)
* Pre-determined time period
Videocrypt enables smart cards to be pre-programmed to suit the
specific programming requirements.
Smart card - providing the revenue security
Security can be addressed on a multitude of levels when using the
smart card. These include:
Chaining
An existing customer would receive a new card which contains part of
the new code, the remainder of the code would be transmitted when
the card is inserted into the decoder and the subscriber compiles
with the instructions contained within the on-screen graphics.
Over-the-air addressing
Systems operators can now address individual subscribers, which is a
vast improvement over other scrambling systems. The operator can
provide additional services, reduce service entitlements, send
individual messages, blacklist and/or whitelist viewers.
Cloning
A number of steps have been taken to stop smart cards being copied
or cloned. A physical deterrent is the first line of defence, and
the integrated circuit contained within the card makes "probing"
very difficult as the IC is likely to become damaged in the process.
Cost is a second factor which is likely to deter manufacturers of
illegal decoders. A considerable amount of time, trouble and
expensive resources would be required to clone the card.
The manufacturers of Videocrypt recommend that the cards are re-
placed every six months, and each time this is done a "secret en-
crypting algorithm" will be changed. Any pirate decoders manufac-
tured during this time would be relatively useless.
And should a pirate decoder be manufactured, it will contain a
unique security code, which could be blacklisted by the systems
operator once the code has been discovered - leading to calls of
complaint by angry customers.
Video taping
Videocrypt offers an simple method of tracking down pirates who
video high-value programming and then distribute it.
The customers unique number can be displayed on the unencoded screen
for reference and future litigation. Although an on-the-screen
code can be generated for signals piracy in a public place, the
codes can be hidden in the picture - and retrieved by a technician
at a later stage.
Videocrypt-your flexible friend?
Videocrypt can be used in a number of applications other than tv
signals protection. They include:
Messaging, messages can be transmitted to individual subscribers or
to a group, so target messaging is now a potential. Messages like:
"Satellite owners in LONDON call 081 XXX XXXX now for a great bar-
gain".
Selling, sales over the air can be utilised with the unique identity
number which verifies an owner and their registered address. Data
can be matrixed with a user personality during ad-breaks to tailor-
make the advertisement.
A unique transaction alphanumeric can be displayed on the TV screen,
and the subscriber will telephone a given number and quote the
alphanumeric - and the deal can then be completed in total security.
SCRAMBLING
The majority of scrambling systems currently on the market are
dependent on analogue processing circuitry, and it is a hard task to
get a secure system without picture deterioration.
Videocrypt can encode and decode a picture without degradation.
The crux of the scrambling system evolves around a patented develop-
ment of Active Line Rotation (Cut and Rotate principle).
Every line of the signal is cut at a number or points along its
length, and this is chosen at random by a 60 bit psuedo random
binary sequence generator (PRBS). As each cut point differs from
the next the signal has no viewing value to an unauthorised recipi-
ent, but authorised recipients decoders recode the picture so that
the true state of the unscrambled line is always first out for
display.
The PRBS is re-seeded at times too, to enhance the security of the
system even more.
Before this ALR process can take place, the decoder needs to be
aware of the cut point on each of the transmitted lines, this is
provided within the encryption process. Each decoder utilises an
PRBS which reflects the characteristics of the system so that the
two halfs can be synchronised and a viewable picture displayed.
Data is transmitted in a series of over-the-air packets, which looks
like:
SYSTEM-----SMART or BLACKLIST
The system comprises of system data included Fiat-Shamir identifica-
tion information, on-screen display messages, fingerprinting and
blacklisting data.
The smart card packet comprises of:
HEADER-----ENCRYPTED DATA-----CHECKSUM
The Videocrypt encryption system is based around a tightly-guarded
secret which has defeated system hackers throughout the world. A
final control algorithm is central to the systems security and this
can be changed at will if the system has been hacked.
Complex calculations are performed within the system in order not to
compromise its security.
But hackers who have attempted to hack the decoder will be disap-
pointed - as there are no secrets held within the system.
Smart Cards
The smart card offers great flexibility to the programme controller
and the viewer alike, and is the key to the Videocrypt system.
The Integrated circuits incorporated within the smart card have a
lot of power and contain EPROM elements which are partially burned
during their manufacture. The ICs are buried within the design to
make the system harder to penetrate.
Smart card block diagram
------- ------- -------
VCC -> - RAM - - ROM - -EPROM-
------- ------- -------
^ ^ ^
TO AND FROM
-------------------------------
GND -> - INTERNAL BUS -
-------------------------------
TO AND FROM
------- ------- -------
-8 BIT- -ANTI - -S/WRE-
RST -> -CPU - -FRAUD- -CNTRL-
- - -DVCES- -I/FCE-
------- ------- -------
CLK VPP I/O
Over the air addressing
Algorithmic information is transmitted to the viewer over the air,
encrypted within the Videocrypt system.
This data is transmitted within the Vertical Blanking Interval (VBI)
and four lines are employed for active data and two others, one
white and one black (for test purposes).
An application of Non Return To Zero (NRZ) with an constant energy
spectrum maximises the systems characteristics.
Four picture-sustaining techniques are used to ensure a high quality
picture. Bit interleaving, hamming codes, quadruple repetition and
check sums are used within the process.
The system can cope with fringe reception areas and will still
function correctly with high levels of noise.
Picture quality
Picture quality is paramount for any scrambling system and due to
the standard being of a digital origin, integrity of the signal is
maintained throughout the encryption and de-encryption process.
Amplitude sampling is conducted by the decoder and a 14MHz internal
clock ensures jitter-free pictures and unstable framing. A digi-
tally derived Automatic Gain Control (AGC) is also included within
the receiver.
Scrambling Sound
Videocrypt also has the capability of encrypting sound sources to
enhance the security of premium events. To date this level of
security has not been utilised by broadcasters.
The system of spectrum inversion renders the sounds received without
authorisation worthless. Videocrypt transposes the frequencies
transmitted and this in turn removed distortion of the sound.
CUSTOMERS
The British Sky Broadcasting channels are the first and only client
to use the Videocrypt system in Europe. Sky Movies was the first
channel to encrypt with Videocrypt on 05/02/90. The Movie Channel
and Sky Sports commenced encryption in April 1991, following the
launch of Astra 1B
In August 1990 an order for 10,000 Videocrypt decoders were ordered
for an Asian satellite television network called Topaz.
The British Broadcasting Corporation (BBC) have announced plans to
use Videocrypt on their BBC Select service, and a number of other
stations are actively considering its use on satellite links,
although no other intentions have been made.
APPENDICES
Technical Data
(supplied by Thomson Consumer Electronics, 1991- subject to change)
VIDEOCRYPT BASEBAND DECODER
* Stand alone video decoder
* On screen display
* De emphasis switch
* Authorise button
* Integrated smart card reader
* Power indicator
PAL MODEL
Video input level IV +/- 3dB flat and clamped
Baseband input level 250 mV +/- 3dB, unclamped level
measured at pre-emphasised transition
frequency
Suitable de-emphasis CCIR 405-1
Video output level IV p.p. into 75 ohms
Video bandwith 50Hz - 4.8 Mhz -3dB typical
Line tilt _ 67dB
Chrominance luminance:
intermodulation _ 5.8 Mhz
Output DC level 300 mV +/- 50 mV
Sampling frequency rejection >- 50dB at 14 Mhz
Number of bits per sample 10
CONNECTIONS
Connections to security comp RS232
Local VT100 terminal ditto
Video in BNC 75 ohm
Scrambled video out BNC 75 ohm
MISC
Local terminal functions are to
show working parameters
give warnings
control local
remote
autonomous
Select scrambling mode
clear
free access
control access
Mains input low pass filtering
Audio scrambling using spectrum
inversion 0dB/600 ohm (optional)
ENDS
------------------------------------------------------------------------
Quotes from INSIDE DIRECTV's IRD, Satellite Retailer, March 19
"The technology is owned by News Datacom, which is a wholly owned
subsidiary of News Corporation (whose operations include FOX BROADCASTING
((as in NFL backhauls)), Twentieth Century Fox Film, and a 50 percent
interest in British Sky Boradcasting Ltd.). The "zero knowledge"
authentication technology which supports the VideoGuard and VideoCrypt
systems were developed by Professor Adi Shamir, professor of applied
mathematics at the Weizman Institute in Rehovet, Israel, and Dr. Amos
Fiat. It is this algorithm, along with more traditional encryption
schemes, like DES, which form the technological foundation of the system.
The VideoCrypt decoder is itself based on a cut and rotate method of
scrambling. According to Dr. Dov Rubin, technical director for the
Israel-based News Datacom, the encoder selects lines at random points
within the television picture at the exact moment of transmission. The
lines are reversed and broadcast so the picture is unintelligible. The
specific location of the encoder's cut points is proprietary and critical
to the security of the unit. As such, the VideoCrypt system employs
"special techniques" to disguise the cut points. The location of the cut
points is fed into the system through the Security Encoder Computer by
way of a card reader and smart card. This PC also accepts input from the
Security Database Computer which acts as an interface to the Subscriber
Management System and the program scheduling system. The Security
Encoder Computer generates packets of data which combine program
identification and scheduling information with a random number. The
packets of data are fed to the smart card, which processes the
information through a secret algorithm to produce a seed for the Pseudo
Random Bit Sequencer (PRBS). This process produces a string of eight-bit
numbers, which determine the cut point for each line. The packets of
information fed to the card are also transmitted over the air. There are
no secrets in this information. The decoder extracts these data packets
and feeds them to the smart card in the decoder, which contains the same
algorithms as the smart card in the encoder. The same seed is therefore
produced, and a similar PRBS reproduces the same cut points, allowing the
decoder to cut the lines in the same place as the encoder and
reconstitute the picture..........Imperative to the security of the
system is that the starting number is "hidden" from view. In essence,
the VideoCrypt smart card is an active security device. it is not
something that passively holds keys, as does the other systems. The
purpose of the VideoCrypt smart card is intrinsically tied to the process
of authorization. Therefore, when the smart card is changed and replaced
by a programmer for any reason, including a break in the security of the
system, the entire decryption/authorization process may be redesigned and
re-issued without affecting the utilization of the decoder."
"As an example ((of NDC advanced techniques)), VideoCrypt uses the
Fiat-Shamir zero knowledge algorithm, which allows the decoder "to
determine if the card inserted in the decoder is valid." According to the
company, the zero knowledge characteristics of the decoder stops the
proliferation of cloned cards should any one card be compromised. Adding
further to the pirate's cost is the type of micro-processor used in the
smart card. The processor is itself secure which means that it is not
easy to read the information stored on the card or monitor the data which
flows from the card to the decoder. A special and expensive electron
microscope would be required to dismantle the microprocessor and "in most
cases, the electron microscope would destroy the charge before the pattern
could be determined," says News Datacom."
"The strategy ((issuing new smart cards)) seems to have worked as there
have been no reports of a pirated VideoCrypt since its entrance into the
market in 1989. VideoCipher, on the other hand was pirated within six
month of its introduction in 1986."
"What's most interesting about VideoCrypt, which is designed and
manufactured by News Datacom, is that while the product appears to be more
secure than VideoCipher, its cost is appreciably less. A direct cost
comparison is hard to come by. However integrated receiver descramblers
in the US sell for between $700-$1500 compared to $260 in England, and a
US dishowner upgrading to the VideoCipher RS will plunk down between $300
and $400, while the decoder portion of the Sky Television receiver amount
to under $150."